How to convert nullable variable to non nullable type?

Question

I have function which will receive parameter ?string

public function func(?string $x): string
{
    $x = trim(strtolower($x));
    $x = preg_replace('/\s+/', ' ', $x);
    $x = str_replace(' ', '-', $x);
    return $x;
}

running ./vendor/bin/phpstan analyse give those errors:

Parameter #1 $str of function strtolower expects string, string|null given.              
Parameter #3 $subject of function preg_replace expects array|string, string|null given.  
Parameter #3 $subject of function str_replace expects array|string, string|null given.   

strtolower needs string and preg_replace&str_replace need array|string

what is the best way to solve this without changing param from ?string $x to string $x?
in otherwords how to change var type from string|null to string ?

Answer 1

I believe you may be able to typecast your value of $x,

example:

function foo(?string $x) : string {
    $a = (string) $x;

    return $a;
}

This should yield,

var_dump(foo("test"));

string(4) "test"

And,

var_dump(foo(null));

string(0) ""

Hope this is what you were looking for.